Download Strategies for Managing Early Succession Habitat for Wildlife

Weed Technology 2007 21:932–937
Strategies for Managing Early Succession Habitat for Wildlife
Craig A. Harper*
Early succession plant communities consisting of a diverse mixture of grasses, forbs, and scattered shrubs are required by
a variety of wildlife species. Early seral stages follow some form of disturbance but can become dominated by shrubs and
trees rather quickly, especially in areas with abundant rainfall and relatively long growing seasons, such as the southeastern
United States. In the absence of natural disturbance regimes, the quality and maintenance of these plant communities for
wildlife is largely dependent upon management. Prescribed fire, disking, herbicide applications, and mowing are practices
commonly used to maintain early succession plant communities for various wildlife species throughout this region.
Prescribed fire consumes vegetative debris, provides open structure at ground level, and facilitates travel and foraging for
wildlife throughout the field. Burning during the dormant season may promote cool-season grasses if they are present in
the field. Burning in late March or early April generally promotes warm-season grasses and forbs. Late growing-season fire
(September) will reduce woody encroachment and may encourage additional forb cover. Disking promotes vegetation
decomposition, provides open structure at ground level, and generally promotes annual plant species. Disking in the fall
and winter stimulates more forb growth than disking in the spring, which will stimulate undesirable nonnative warmseason grasses if present in the seedbank. Selective herbicides can influence plant composition and can be used to encourage
grasses where forbs dominate, to promote forbs where grasses dominate, and to reduce woody cover. Mowing during
midsummer encourages additional grasses in fields dominated by forbs but is not recommended for field maintenance
because mowing produces thatch, which limits the ability of several wildlife species to travel and forage through the field,
suppresses the seedbank, and destroys nests and young wildlife. Several practices can be used in combination to meet
specific objectives. Succession should be set back every 2 to 4 yr, depending on plant response and focal wildlife species. It
is important to intersperse disturbance in space and time, so that a variety of cover types are always available, even to those
animals with small home ranges.
Key words: Disking, early succession plant communities, grassland songbirds, mowing, native warm-season grasses,
northern bobwhite, prescribed fire.
Changing land-use practices and the suppression of fire has
drastically altered the landscape of the American South, as
well as other regions of the United States. These changes have
led to a net loss of native early succession plant communities
required by many wildlife species (Brennan 1991). As a result,
wildlife populations dependent on these communities have
suffered (Hunter et al. 2001). Efforts to restore native early
succession plant communities (most notably several programs
offered through the Farm Bill) have been successful in many
areas and increases in wildlife populations have been recorded
(Delisle and Savidge 1997; Gill et al. 2006; Marcus et al.
2000). However, through this process, landowners and
managers have recognized early succession plant communities
(dominated by herbaceous species) become midsuccession
communities (dominated by woody species) rather quickly if
some disturbance regime is not implemented to set back
succession (Dykes 2005; Lorimer 2001). This is especially true
in areas with relatively long growing seasons and abundant
precipitation (. 30 inches of rainfall per year) and where
winged-seeded woody species, [e.g., sweetgum (Liquidambar
styraciflua L.), green ash (Fraxinus pennsylvanica Marsh.),
winged elm (Ulmus alata Michx.), red maple (Acer rubrum
L.)], are present. As succession marches forward, habitat
quality declines for many wildlife species.
DOI: 10.1614/WT-07-024.1
* Associate Professor, Department of Forestry, Wildlife, and Fisheries,
University of Tennessee, Knoxville, TN 37996. Corresponding author’s E-mail:
[email protected]
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The quality of early succession wildlife habitat is dependent
on the composition and structure of the plant community
(Harper et al. 2007). For a few wildlife species, such as eastern
meadowlarks (Sturnella magna Linnaeus) and Henslow’s
sparrows (Ammodramus henslowii Audubon), a field composed primarily of native grasses, such as broomsedge
bluestem (Andropogon virginicus L.) and little bluestem
[Schizachyrium scoparium (Michx.) Nash], may represent
quality habitat (Giocomo 2005). However, for many other
wildlife species, a more diverse vegetative community provides
optimum habitat conditions (Burger et al. 1990; Millenbah et
al. 1996).
The presence of forbs and scattered brambles and shrubs,
along with native grasses, enhances nesting and brooding
cover and produces a quality food source for many wildlife
species. The importance of these plants cannot be overstated.
Forbs, such as common ragweed (Ambrosia artemisiifolia L.),
pokeweed (Phytolacca americana L.), beggarslice [Hackelia
virginiana (L.) I.M. Johnston], partridge pea [Chamaecrista
fasciculata (Michx.) Greene], and native lespedezas, such as
slender [Lespedeza virginica (L.) Britt] and hairy lespedeza
[Lespedeza hirta (L.) Hornem.], provide forage and seed used
by many wildlife species. These forbs also provide a protective
umbrella canopy of cover that is open underneath and used
extensively by northern bobwhite quail (Colinus virginianus
Linnaeus) and wild turkey (Meleagris gallopavo Linnaeus)
broods, as well as many ground-feeding songbirds (Burger
2000; Roseberry and Klimstra 1984). Scattered thickets of
blackberries (Rubus spp.), wild plum (Prunus spp.), and the
occasional sumac (Rhus spp.) motte offer diverse nesting cover
for dickcissels (Spiza americana J. F. Gmelin), field sparrows
(Spizella pusilla Wilson), and other birds that may nest in
shrub cover (Giocomo 2005). These woody shrubs also
provide critical winter cover and a quality food source for
many wildlife species.
Maintaining early succession and balancing the composition of grass, forbs, and shrubby cover in a field is not
necessarily easy. Managing for 30 to 70% native grass cover
and 30 to 70% forb cover, with shrub cover no more than
100 yards apart, may be the ideal composition for a diversity
of wildlife dependent on early succession plant communities.
However, continued management, knowledge of successional
patterns, persistence, and a different perspective by the
traditional landowner are required.
Management Techniques
Several management practices enable landowners to set
back succession; however, not all practices are equal in the
quality of the resulting habitat (Harper et al. 2007). The type
of disturbance practice and its timing, frequency, and
intensity influences plant composition, structure, and successional trajectory, which strongly influence habitat quality for
wildlife.
Most landowners manage fields by mowing (Dykes 2005).
Relatively few are willing to burn fields because of liability and
the general fear of fire. Few landowners manage fields by
disking because they are unaware of the benefits. Most
property owners are reluctant to use herbicides because of
their fear of chemicals and their ecological concerns. In the
South, there is little native grass and forb acreage managed by
grazing because almost all livestock producers in the region
use nonnative forages (Ball et al. 2002; Fribourg et al. 1988).
Mowing. Mowing (or bushhogging) is the traditional practice
used to maintain early succession habitat, which is unfortunate because mowing creates undesirable conditions for
wildlife. When vegetation is cut and not removed from the
field, a deep thatch layer is created at ground level (McCoy et
al. 2001). Deep thatch restricts travel for game bird chicks and
limits the ability of broods to feed on seed and invertebrates
(Burger et al. 1990; Hurst 1972). Vegetative diversity is also
reduced when the seedbank is suppressed by thatch (Gruchy
2007), which acts as an effective blanket over the field.
To compound the negative effects of mowing, most
landowners mow during summer and again in the fall just
before winter. These are the worst possible times for wildlife!
When fields are mowed in the summer, nests and nestlings are
destroyed, white-tailed deer (Odocoileus virginianus Zimmermann) fawns and young cottontail rabbits (Sylvilagus
floridanus J. A. Allen) are often killed, and reproductive cover
is destroyed at a time when it is needed most. Ironically, many
of these same landowners then blame predators, such as redtailed hawks (Buteo jamaicensis J. F. Gmelin), for reducing
wildlife populations, such as bobwhites, as they wipe clear
available cover for nesting and brood rearing. When fields are
mowed in the fall, protective cover that would be used
through winter is removed, drastically reducing usable space
for many wildlife species. If fields must be managed by
mowing, the job should be completed in late winter, just
before spring green-up, which would provide cover throughout winter and not disrupt the nesting season.
Another irony associated with field mowing is that mowing
is not effective in reducing woody competition, which is the
main reason landowners mow fields. Mowing generally
stimulates sprouting, and overall, woody encroachment is
not reduced (Gruchy et al. 2007; Johnstone 1990).
Mowing can be a useful tool for meeting certain objectives
but should not be considered the primary method of
maintaining an early succession plant community. Fields
primarily composed of perennial forbs, such as goldenrods
(Solidago spp.) and blackberry, can be improved for several
ground-nesting birds by mowing strips in midsummer.
Mowing at that time will encourage warm-season grass growth
(Hazell 1965). Native warm-season grasses, such as broomsedge
bluestem, provide critical nesting cover for bobwhites (Dimmick 1971). Although mowing may disrupt the nesting activity
of various songbirds in those strips, the whole field is not
mowed, only a small percentage of the overall acreage (certainly
no more than one-fourth). The increase in grass will not only
provide additional nesting cover in the future for other species
but also enable the landowner to implement the most desirable
management practice—prescribed fire.
Burning. As recently as the early 20th century, it was
common practice in the American South to burn fields and
woods in an effort to increase the palatability of vegetation for
grazing and to expose chestnuts and acorns in the woods for
ranging hogs and game (Pyne 1982). Unfortunately, prescribed fire is no longer implemented as in yesteryear, partly
the result of misguided propaganda sponsored by the U.S.
Forest Service from 1927 to 1930 (‘‘Dixie Crusaders’’) and
partly a lack of understanding and knowledge of how to use
fire and its effects on natural communities (Donovan and
Brown 2007; Johnson and Hale 2000; Riebold 1971).
Unlike mowing, fire cleans the field of debris, creates an
open structure at ground level, and stimulates the seedbank to
germinate (Buckner and Landers 1979; Gruchy 2007;
Komarek 1963), increasing vegetative diversity and making
seed and invertebrates available for game bird broods (Hurst
1972). Prescribed fire enables upland wildlife, often perceived
as needing edge habitats (see Guthery 1997), to travel
throughout the entire field, not just the field edges. Burning
can also increase nutrient availability as rain carries nutrients
from the ash down into the top layer of soil (Wright and
Bailey 1982).
Despite the benefits of burning, fire must be used with care,
and practitioners should be familiar with, and adhere to, state
prescribed fire laws (see Sun 2006). Disked firebreaks of
exposed soil must be established around the area to be burned,
and burning should be undertaken by experienced personnel
and under proper environmental conditions. Landowners who
wish to manage their fields with fire should contact their
state’s forestry and wildlife agencies for possible assistance.
Forestry and wildlife professionals will help landowners
prepare a management plan. Some forestry agencies (and
private operators) will implement a burn for a fee; some will
help for free. Another source of assistance is the local
volunteer fire department. It is not uncommon for these
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volunteers to come out and assist landowners when burning
a field or woodlot. And it is always important to inform the
local fire department before burning even if they are not
assisting with the burn.
Timing of burning is most important to meet certain
objectives. Most fields are burned January through March.
This may not be desirable timing for a few reasons. Burning
early in the dormant season can stimulate and increase
nonnative cool-season grasses by clearing the field just before
those grasses begin active growth (March) (Ewing and Engle
1988). A primary objective of landowners wanting to improve
early successional cover should be to eradicate nonnative
perennial cool-season grasses [e.g., tall fescue (Festuca
arundinacea Schreb.), orchardgrass (Dactylis glomerata L.),
bromegrasses (Bromus spp.), and velvetgrass (Holcus lanatus
L.)], which displace desirable native grasses and forbs, reduce
vegetative diversity by inhibiting seedbank germination, and
limit travel and food availability for young game birds and
ground-feeding songbirds (Barnes et al. 1995). Burning early
in the dormant season also reduces cover at a time when it
may already be limited.
Burning later in the dormant season (late March to early
April) stimulates warm-season grasses (Gruchy 2007; Towne
and Owensby 1984) and helps reduce cool-season grasses that
have already started growing (Howe 2000). Burning in the
late dormant season or early growing season (through midApril) not only stimulates desirable warm-season grasses and
forbs (Buckner and Landers 1979) but also allows wildlife to
use the cover in the field throughout winter before spring
green-up. This is also before the nesting season, which begins
in late April to early May for birds that nest in the field
(Giocomo 2005). Burning in the late growing season
(September) effectively reduces woody encroachment equal
to various herbicide applications (Gruchy et al. 2007).
Burning at this time top-kills woody stems before carbohydrates are transported from the leaves to the root system in
preparation for senescence. Therefore, root systems are
depleted of the energy needed to resprout.
Frequency of burning should be dictated by desired
vegetation response. Fire return interval will determine the
composition and structure of the subsequent plant community. Annual prescribed fire will shift the plant community
to a more grass- and forb-dominated composition, whereas
a 2- to 3-yr burning rotation generally produces an herbaceous community with scattered shrubs. A 3- to 4-yr
fire-return interval will create a mixed grass and forb
community with a substantial shrub component. A firereturn interval that maintains grasses and forbs for nesting
and brood rearing, allows soft mast production from blackberries and other species, and provides winter cover will
enhance habitat conditions for a wide variety of wildlife
species.
Disking. The savannas and oak (Quercus spp.) woodlands
once present across the South were regularly set back by fire.
They were also disturbed by the action of hooves, primarily
those of buffalo (Bison bison Linnaeus) and elk (Cervus elaphus
Linnaeus). This hoof action is also evident in modern-day
pastures with domestic cattle (Bovidae spp. Gray) and horses
(Equus caballus Linnaeus).
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Disking can be used to mimic the natural disturbance of
buffalo and elk and provide multiple benefits. Unlike
mowing, disking creates an open structure at ground level
and facilitates decomposition (Gruchy 2007). The soil
disturbance stimulates the seedbank to germinate and
increases vegetative diversity (Buckner and Landers 1979).
Readily stimulated by disking, and particularly attractive for
bobwhites, are several annual forbs, such as partridge pea,
common ragweed, tropic croton (Croton glandulosus L.),
Florida pusley (Richardia scabra L.), and annual sunflowers
(Helianthus spp.). Several perennial species, including the
native lespedezas, beggarslice, pokeweed, and spurred butterfly
pea [Centrosema virginianum (L.) Benth.], can also be
stimulated by light disking, especially if preceded by
prescribed fire (Rosene and Freeman 1988). Disturbed soil
enables birds to dust themselves, which helps reduce external
parasites.
Fields planted to native warm-season grasses often become
dominated with grass over time (Dykes 2005; Millenbaugh et
al. 1996). This is not desirable for wildlife because of the
importance of forbs. Disking is the best management practice
to stimulate additional forb cover (Buckner and Landers
1979; Gruchy 2007). Disking at different times, however, can
influence vegetation composition (Gruchy and Harper 2006;
Smith 2006). Dormant-season disking, before April, generally
encourages increased forb cover, whereas disking into April
and May encourages undesirable nonnative grasses, such as
johnsongrass [Sorghum halepense (L.) Pers.], crabgrass (Digitaria spp.), and broadleaf signalgrass [Brachiaria platyphylla
(Munro ex Wright) Nash], if they are present in the seedbank
(Gruchy and Harper 2006). When undesirable species are
suspected, a selective PRE herbicide application (such as
imazapic) following disking may be used to control undesirable species.
Heavy offset disks are more efficient at reducing native
grass cover than lighter tandem disks. Burning or mowing is
often necessary before disking with a light tandem disk
because the disk will not cut through the grasses. Burning is
recommended. Disking following burning is much easier than
trying to break down thatch left by mowing. Many passes may
be necessary to break up and incorporate 25 to 50% of the
vegetation following mowing.
Disking on rotation is an important consideration.
Depending on vegetation response, fields can be managed in
thirds or fourths by disking strips approximately 50 feet wide
each year and leaving two or three 100- to 150-feet-wide strips
undisked in between.
Herbicides. Early succession plant communities should not
be maintained with herbicides, but the use of herbicides is
important in managing vegetation composition, especially
when nonnative, invasive species are present. This is most
critical when restoring fields covered with nonnative grasses,
such as tall fescue or bermudagrass [Cynodon dactylon (L.)
Pers.]. It is necessary to eradicate this ‘‘blanket’’ of cover
before a composition of desirable plant species and structure
can be established. Spraying glyphosate in the fall is
recommended to kill cool-season grasses (Fribourg et al.
1988; Gruchy 2007; Smith 1989; Vogel and Waller 1990),
and imazapyr has been used successfully to eradicate
bermudagrass just before or when it flowers (Bond et al.
2005).
Careful attention should be given to the seedbank after
eradicating undesirable grass cover. Often, desirable vegetation establishes without the need for planting (Gruchy 2007).
Burning and/or disking after the undesirable grass cover is
controlled will stimulate germination of the seedbank.
Planting native warm-season grasses is not needed for early
succession wildlife habitat when some, such as broomsedge
bluestem, are already present on the site.
Herbicide applications may be broadcast full, with alternate
nozzles closed, or spot-sprayed. Full-broadcast applications are
necessary when restoring fields covered with nonnative grasses.
However, alternate (or one out of three) nozzles can be closed
when spraying a field that has become too dense with native
grass (70 to 100% cover). Best results are realized when native
grasses are sprayed when they are only 6 to 12 inches tall,
usually in mid- to late April, and if undesirable grasses have
been eradicated. Spraying grasses taller than 12 inches will
increase problems with thatch. If undesirable grasses are
waiting in the seedbank, they will be released by alternatenozzle spraying. If undesirable grasses have been eradicated,
alternate-nozzle spraying will kill strips of dense native grass
across the field and enable desirable warm-season forbs (such
as pokeweed, ragweed, and partridge pea) to germinate and
establish among the grass.
Spot applications are especially useful for eradicating
unwanted, woody growth. Winged elm, sweetgum, green
ash, locusts (e.g., Robinia pseudoacacia L.), and red maple can
be problematic and take over a field quickly if not controlled.
Imazapyr and triclopyr have been used successfully to reduce
woody encroachment in early succession plant communities.
Problem species and objectives for vegetation composition
may dictate which herbicide to use. For example, imazapyr
does not effectively control legumes or winged elm. Triclopyr
may not effectively control yellow poplar (Liriodendron
tulipifera L.), sourwood (Oxydendrum arboreum L.), hickories
(Carya spp.), or Chinese privet (Ligustrum sinense Lour.).
Further, triclopyr kills forbs but does not kill native warmseason grasses. Imazapyr promotes blackberries and legumes
but may kill native warm-season grasses (Bond et al. 2005;
Gruchy et al. 2007).
Grazing. Wildlife associated with early succession plant
communities throughout the South evolved with grazing
ungulates. Grazing can be used to effectively manage native
grasses and associated vegetation. Managing grazing intensity,
however, is critical. Grazing should be initiated before
flowering when native warm-season grasses reach approximately 24 inches in height, depending upon species. Cattle should
be removed once the grasses are grazed down to 10 to
12 inches. If native grasses are overgrazed, grass density will
decline. Desirable winter cover for wildlife will be reduced or
eliminated if native warm-season grasses are grazed past early
August (Harper et al. 2007).
Another strategy is patch-burn grazing, whereby 1/4 to 1/3
of the pasture is burned annually (late dormant season) on
rotation. Livestock are free to use the entire pasture during the
growing season, but selectively graze the section most recently
burned. Unburned sections provide nesting cover for various
songbirds and upland game birds, while the burned and
grazed section is used for brooding.
Management Strategies
To have a positive influence on early successional wildlife
populations, management strategies must go beyond singlefield applications and involve multiple fields on a landscape
level. Landowners must do their part by providing as much
usable space on their property as possible and doing so in an
arrangement that necessitates less travel by wildlife to meet
their habitat requirements. There are specific strategies to
improve the arrangement and condition of habitat within and
across fields.
Managing Within the Field. Most fields are managed as
a single unit; that is, the entire field is managed the same way
at the same time. Depending on the species of interest, the
number of fields, and amount of acreage present in early
succession, whole-field management may not be desirable.
Where fields are fairly large (. 4 ha) and relatively square in
shape, breaking the field into two or more units may be
desirable, depending upon the focal wildlife species and the
management practice used. Grassland songbirds, especially
grasshopper sparrows (Ammodramus savannarum J. F. Gmelin), typically prefer larger fields ($ 40 ha) (Dykes 2005;
Giocomo 2005), whereas other species, such as bobwhite quail
and cottontail rabbits, do not necessarily require large fields,
and positive population responses can be realized by
establishing field borders around crop fields and managing
whole fields of 2 to 4 ha.
If a field is managed by disking in thirds, breaking the field
into sections may not be a real benefit (depending upon field
size and the width of disked strips). However, if the field is
managed with prescribed fire, breaking the field into sections
allows different sections to be managed on a different
rotation. Whole sections may also be disked on rotation,
which would be similar to very wide disked strips (150 feet) if
a large field was managed by disking in thirds. As an example
of managing in sections, a 4-ha field with four 1-ha sections
allows one section to be burned or disked each year on a 4-yr
rotation, providing diverse structure across the 4-ha field. This
is important if there are few fields on the property or if there is
relatively little acreage overall in early succession cover.
According to vegetation composition within the field,
structure may be diversified by establishing hedgerows
containing desireable shrubs [e.g., wild plum sumac and
elderberry (Sambucus canadensis L.)] to distinguish field
sections.
Managing Across Fields. On properties that contain several
fields, instead of dividing the field and managing sections,
whole fields may be burned or disked on rotation. However,
proximity of fields should be considered carefully when
deciding whether to manage whole fields or sections. Early
succession plant communities should be well interspersed
throughout the property for maximum benefit for wildlife
dependent upon this seral stage. If fields are widely separated,
managing whole fields should be discouraged. Juxtaposing
fields or sections of fields burned or disked recently with those
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in the middle of a rotation is most important. It is critical that
all available cover is never set back in one year.
The other major consideration when managing for early
successional wildlife is the availability of native early
succession plant communities in the surrounding landscape.
This is especially important for grassland songbirds and
bobwhite quail. Grassland songbirds, such as grasshopper
sparrows, prefer a considerable percentage (roughly 50%) of
the surrounding landscape in grassland habitat. Quail and
rabbits also benefit greatly if the surrounding landscape is
comprised largely of quality early succession habitat, as
opposed to fields of nonnative perennial cool-season grasses or
forest. It is important for landowners to realize, providing an
island of attractive habitat in a sea of nonhabitat will not
produce a positive long-term effect for many early succession
obligates. Landowners interested in these species should form
area cooperatives with common goals and objectives with
regard to providing and maintaining high-quality early
succession habitats.
Conclusions
Populations of many wildlife species associated with early
succession plant communities have declined precipitously
across the eastern United States over the past 50 yr. These
declining species vary greatly with respect to reproductive and
feeding strategies. These species include birds, mammals,
reptiles, amphibians, and even invertebrates. They are found
in various physiographic provinces, from the coastal plain, to
the highest elevations in the Appalachians. Many specific
habitat types are included in their ranges, but there is one
common theme—all of them rely on an early seral stage. And
native early succession plant communities are disappearing
without proactive management.
Several management practices can be used to maintain early
succession plant communities. Nonetheless, there are two
primary threats—nonnative species and landowner perspectives. Before native early succession plant communities can be
created or restored, it is critical that many nonnative plants be
eradicated from the site. This often requires extended effort
and persistence. Landowners wishing to improve conditions
for wildlife that require early seral stages must change the way
they view ‘‘weeds’’ and tall grass. What has been regarded
‘‘unkempt’’ over the years must be seen as desirable, managed
habitat. Quality early succession wildlife habitat does not
appear clean and even as the nonnative pastures and hayfields
established through much of the twentieth century.
Acknowledgments
I thank John Gruchy, James Giocomo, and an anonymous
reviewer for providing constructive comments and suggestions
on an earlier draft of this paper.
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Received February 14, 2007, and approved June 3, 2007.
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